331 lines
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331 lines
7.3 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of MCHECK</TITLE>
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</HEAD><BODY>
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<H1>MCHECK</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2019-03-06<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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mcheck, mcheck_check_all, mcheck_pedantic, mprobe - heap consistency checking
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/mcheck.h">mcheck.h</A>></B>
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<B>int mcheck(void (*</B><I>abortfunc</I><B>)(enum mcheck_status </B><I>mstatus</I><B>));</B>
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<B>int mcheck_pedantic(void (*</B><I>abortfunc</I><B>)(enum mcheck_status </B><I>mstatus</I><B>));</B>
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<B>void mcheck_check_all(void);</B>
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<B>enum mcheck_status mprobe(void *</B><I>ptr</I><B>);</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>mcheck</B>()
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function installs a set of debugging hooks for the
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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family of memory-allocation functions.
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These hooks cause certain consistency checks to be performed
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on the state of the heap.
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The checks can detect application errors such as freeing a block of memory
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more than once or corrupting the bookkeeping data structures
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that immediately precede a block of allocated memory.
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<P>
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To be effective, the
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<B>mcheck</B>()
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function must be called before the first call to
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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or a related function.
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In cases where this is difficult to ensure, linking the program with
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<I>-lmcheck</I>
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inserts an implicit call to
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<B>mcheck</B>()
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(with a NULL argument)
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before the first call to a memory-allocation function.
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<P>
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The
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<B>mcheck_pedantic</B>()
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function is similar to
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<B>mcheck</B>(),
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but performs checks on all allocated blocks whenever
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one of the memory-allocation functions is called.
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This can be very slow!
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<P>
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The
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<B>mcheck_check_all</B>()
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function causes an immediate check on all allocated blocks.
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This call is effective only if
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<B>mcheck</B>()
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is called beforehand.
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<P>
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If the system detects an inconsistency in the heap,
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the caller-supplied function pointed to by
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<I>abortfunc</I>
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is invoked with a single argument,
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<I>mstatus</I>,
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that indicates what type of inconsistency was detected.
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If
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<I>abortfunc</I>
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is NULL, a default function prints an error message on
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<I>stderr</I>
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and calls
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<B><A HREF="/cgi-bin/man/man2html?3+abort">abort</A></B>(3).
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<P>
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The
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<B>mprobe</B>()
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function performs a consistency check on
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the block of allocated memory pointed to by
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<I>ptr</I>.
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The
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<B>mcheck</B>()
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function should be called beforehand (otherwise
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<B>mprobe</B>()
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returns
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<B>MCHECK_DISABLED</B>).
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<P>
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The following list describes the values returned by
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<B>mprobe</B>()
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or passed as the
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<I>mstatus</I>
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argument when
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<I>abortfunc</I>
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is invoked:
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<DL COMPACT>
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<DT id="1"><B>MCHECK_DISABLED</B> (<B>mprobe</B>() only)
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<DD>
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<B>mcheck</B>()
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was not called before the first memory allocation function was called.
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Consistency checking is not possible.
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<DT id="2"><B>MCHECK_OK</B> (<B>mprobe</B>() only)
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<DD>
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No inconsistency detected.
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<DT id="3"><B>MCHECK_HEAD</B>
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<DD>
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Memory preceding an allocated block was clobbered.
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<DT id="4"><B>MCHECK_TAIL</B>
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<DD>
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Memory following an allocated block was clobbered.
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<DT id="5"><B>MCHECK_FREE</B>
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<DD>
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A block of memory was freed twice.
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</DL>
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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<B>mcheck</B>()
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and
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<B>mcheck_pedantic</B>()
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return 0 on success, or -1 on error.
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<A NAME="lbAF"> </A>
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<H2>VERSIONS</H2>
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The
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<B>mcheck_pedantic</B>()
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and
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<B>mcheck_check_all</B>()
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functions are available since glibc 2.2.
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The
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<B>mcheck</B>()
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and
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<B>mprobe</B>()
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functions are present since at least glibc 2.0
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<A NAME="lbAG"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>mcheck</B>(),
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<B>mcheck_pedantic</B>(),
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<BR>
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<B>mcheck_check_all</B>(),
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<B>mprobe</B>()
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</TD><TD>Thread safety</TD><TD>
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MT-Unsafe race:mcheck
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<BR>
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const:malloc_hooks
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<BR></TD></TR>
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</TABLE>
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<P>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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These functions are GNU extensions.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Linking a program with
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<I>-lmcheck</I>
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and using the
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<B>MALLOC_CHECK_</B>
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environment variable (described in
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<B><A HREF="/cgi-bin/man/man2html?3+mallopt">mallopt</A></B>(3))
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cause the same kinds of errors to be detected.
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But, using
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<B>MALLOC_CHECK_</B>
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does not require the application to be relinked.
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<A NAME="lbAJ"> </A>
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<H2>EXAMPLE</H2>
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The program below calls
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<B>mcheck</B>()
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with a NULL argument and then frees the same block of memory twice.
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The following shell session demonstrates what happens
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when running the program:
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<P>
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$<B> ./a.out</B>
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About to free
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<P>
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About to free a second time
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block freed twice
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Aborted (core dumped)
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<A NAME="lbAK"> </A>
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<H3>Program source</H3>
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#include <<A HREF="file:///usr/include/stdlib.h">stdlib.h</A>>
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#include <<A HREF="file:///usr/include/stdio.h">stdio.h</A>>
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#include <<A HREF="file:///usr/include/mcheck.h">mcheck.h</A>>
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<P>
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int
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main(int argc, char *argv[])
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{
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<BR> char *p;
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<P>
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<BR> if (mcheck(NULL) != 0) {
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<BR> fprintf(stderr, "mcheck() failed\n");
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<P>
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<BR> exit(EXIT_FAILURE);
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<BR> }
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<P>
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<BR> p = malloc(1000);
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<P>
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<BR> fprintf(stderr, "About to free\n");
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<BR> free(p);
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<BR> fprintf(stderr, "\nAbout to free a second time\n");
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<BR> free(p);
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<P>
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<BR> exit(EXIT_SUCCESS);
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}
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<A NAME="lbAL"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+mallopt">mallopt</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+mtrace">mtrace</A></B>(3)
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<A NAME="lbAM"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="6"><A HREF="#lbAB">NAME</A><DD>
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<DT id="7"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="8"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="9"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="10"><A HREF="#lbAF">VERSIONS</A><DD>
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<DT id="11"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="12"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="13"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="14"><A HREF="#lbAJ">EXAMPLE</A><DD>
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<DL>
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<DT id="15"><A HREF="#lbAK">Program source</A><DD>
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</DL>
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<DT id="16"><A HREF="#lbAL">SEE ALSO</A><DD>
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<DT id="17"><A HREF="#lbAM">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:48 GMT, March 31, 2021
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</BODY>
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</HTML>
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